The invention is directed to improved methods for the compressive shrinkage of fabrics. The invention is applicable to particular advantage to the treatment of tubular knitted fabrics, but is not to be considered as limited thereto, as the principles of the invention are useful to advantage in connection with the processing of open width fabrics of both knitted and non-knitted construction.
In the processing of knitted fabrics, particularly tubular knitted fabrics, one of the widely utilized and commercially successful procedures for compressive shrinkage treatment is reflected in the Eugene Cohn, et al. U.S. Pat. Nos. 3,015,145, 3,015,146 and 3,083,435. These procedures involve one or, more typically, two compressive shrinking stations, each comprising an opposed pair of rollers and a feeding and confining shoe. Incoming fabric is passed between a feeding roller and a confining shoe, causing the fabric to be advanced at a predetermined speed in a relatively positive manner. The second roller, referred to as a retarding roller, forms a nip with the feeding roller, such that fabric, after it exits from the confining shoe, is engaged under pressure simultaneously between the feeding and retarding rollers. The retarding roller, which is driven at a surface speed controllably slower than the surface speed of the feeding roller, retards the advance of the fabric, so that controlled lengthwise compression of the fabric takes place in a short compressive shrinking zone formed between the roller nip and the terminating edge of the fabric confining shoe. The shoe and/or rollers desirably are heated, such that the emerging fabric retains a substantial portion, at least, of the compressive shrinkage imparted thereto in the compressive shrinkage zone.
Even though the above described compressive shrinking techniques have been extremely successful commercially, there are certain inherent limitations thereto which result from the fact the fabric is being acted upon simultaneously, at the same point but on opposite sides, by rollers operating at different speeds. The opposite sides of the fabric are thus necessarily treated slightly differently. In addition, the inherent slippage of at least the feeding roller relative to the fabric surface at the roller nip sometimes imparts an undesirable surface appearance to certain types of fabrics, such as by lightening darker shades of outerwear fabric, for example, or imparting a shine to underwear fabrics. This can be disconcerting particularly with respect to the processing of tubular fabrics, where the "opposite" sides of the fabric during processing are in fact the same surface of the fabric--namely the outside surface--in the finished garment.
For most applications, the tendency of a single compressing shrinking station of the above described type to have an asymmetrical effect on opposite sides of the fabric is accommodated by providing for dual station machines, with one compressive shrinking station being reversely oriented with respect to the other. This provides acceptable results for some fabrics, for example, but still has shortcomings with respect to highly sensitive fabrics, such as dark shades of outerwear fabrics.
In accordance with the present invention, improved techniques are provided for the mechanical compressive shrinkage of fabrics, particularly but not necessarily tubular knitted fabrics, which enable the many important advantages of the differential roller processing technique to be employed yet which significantly minimizes or eliminates certain inherent limitations in the existing procedures. More specifically, the method of the invention utilizes opposed feeding and retarding rollers, driven respectively at higher and lower surface speeds, for feeding and retarding fabric. However, in contrast to the equipment of the above described patented construction, the respective feeding and retarding rollers are separated by a distance significantly greater than the thickness of the fabric being processed, so that the fabric cannot be engaged simultaneously on opposite sides by the respective rollers. A fabric confining shoe (entry shoe) is associated with the feeding roller, and a separate confining shoe (exit shoe) is associated with the retarding roller. The extremities of these respective entry and exit shoes form between them a defined confinement zone. the fabric is decelerated and longitudinally compressed at the entrance to the zone, and confined and guided for a controlled dwell time during its passage through the zone.
To particular advantage, the opposed extremities of the respective confining shoes are located substantially at the point of maximum convergence of the respective feeding and retarding rollers and are disposed at a substantial angle, such as 45.degree., to the surface of the feeding roller. Accordingly, as the fabric exits the discharge end of the entry shoe, it is abruptly diverted by the leading end of the exit shoe and is guided into the confinement zone, defined between the two shoes. Upon exiting the confinement zone, the fabric is immediately contacted by the outer surface of the retarding roller, travelling at a controllably slower surface speed than the feeding roller.
Significantly, although the feeding and retarding rollers are operated at controllably different surface speeds, the rollers do not act simultaneously upon opposite surfaces of the fabric at the same point, so that it is not necessary for the roller surfaces to have any significant slippage with respect to the fabric surfaces. As a result, it is possible under the present invention to impart the high degree of mechanical compressive shrinkage, required by many knitted fabrics, in a single station machine.
To advantage, fabric passing through the confinement zone is confined under only minimum pressures, in the thickness direction. This is accomplished by providing for a precision, on-th-fly adjustment mechanism for movably positioning one of the shoes, preferably the entry shoe, for limited motion about a pivot axis. This accommodates variation in the thickness of the confining zone during normal operations of the apparatus. The confining pressures acting on the fabric in the zone are maintained at a level sufficient to avoid crimping of the longitudinally compressed fabric, but typically not significantly greater than that.
In one of its particularly preferred embodiments, apparatus used in the practice of the invention has substantial compatibility, structure, with the equipment heretofore marketed under the above mentioned United States patents, and with respect to which there is a substantial installed base of equipment. The apparatus of the invention is capable of being incorporated by a relatively simple retrofit into the existing installed equipment, utilizing much of the existing mechanism, resulting in significant upgrading in performance of the equipment for at least certain types of fabrics.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following description of a preferred embodiment and to the accompanying drawings.